Page 1
ADC0844/ADC0848
8-Bit µP Compatible A/D Converters with Multiplexer
Options
General Description
TheADC0844 and ADC0848 are CMOS 8-bit successive approximation A/D converters with versatile analog input multiplexers. The 4-channel or 8-channel multiplexers can be
software configured for single-ended, differential or
pseudo-differential modes of operation.
The differential mode provides low frequency input common
mode rejection and allows offsetting the analog range of the
converter. In addition, the A/D’s reference can be adjusted
enabling the conversion of reduced analog ranges with 8-bit
resolution.
The A/Ds are designed to operate from the control bus of a
wide variety of microprocessors. TRI-STATE
®
output latches
that directly drive the data bus permit the A/Ds to be configured as memory locations or I/O devices to the microprocessor with no interface logic necessary.
Features
n Easy interface to all microprocessors
n Operates ratiometrically or with 5 V
DC
voltage reference
n No zero or full-scale adjust required
n 4-channel or 8-channel multiplexer with address logic
n Internal clock
n 0V to 5V input range with single 5V power supply
n 0.3" standard width 20-pin or 24-pin DIP
n 28 Pin Molded Chip Carrier Package
Key Specifications
n Resolution 8 Bits
n Total Unadjusted Error
±
1
⁄2LSB and±1 LSB
n Single Supply 5 V
DC
n Low Power 15 mW
n Conversion Time 40 µs
Block and Connection Diagrams
TRI-STATE®is a registered trademark of National Semiconductor Corp.
DS005016-1
*ADC0848 shown in DIP Package CH5-CH8 not included on the ADC0844
June 1999
ADC0844/ADC0848 8-Bit µP Compatible A/D Converters with Multiplexer Options
© 1999 National Semiconductor Corporation DS005016 www.national.com
Page 2
Block and Connection Diagrams (Continued)
Ordering Information
Temperature Total Unadjusted Error MUX Package
Range
±
1
⁄2LSB
±
1 LSB Channels Outline
ADC0844CCN 4 N20A
0˚C to +70˚C Molded Dip
ADC0848BCN 8 N24C
ADC0848CCN Molded Dip
−40˚C to +85˚C
ADC0844BCJ 4 J20A
ADC0844CCJ Cerdip
ADC0848BCV 8 V28A
ADC0848CCV Molded Chip Carrier
Molded Chip Carrier Package
DS005016-29
Top View
See Ordering Information
Dual-In-Line Package
DS005016-2
Top View
Dual-In-Line Package
DS005016-30
Top View
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Page 3
Absolute Maximum Ratings (Notes 1, 2)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Supply Voltage (V
CC
) 6.5V
Voltage
Logic Control Inputs −0.3V to +15V
At Other Inputs and Outputs −0.3V to V
CC
+0.3V
Input Current at Any Pin (Note 3) 5 mA
Package Input Current (Note 3) 20 mA
Storage Temperature −65˚C to +150˚C
Package Dissipation at T
A
=
25˚C 875 mW
ESD Susceptibility (Note 4) 800V
Lead Temperature
(Soldering, 10 seconds)
Dual-In-Line Package (Plastic) 260˚C
Dual-In-Line Package (Ceramic) 300˚C
Molded Chip Carrier Package
Vapor Phase (60 seconds) 215˚C
Infrared (15 seconds) 220˚C
Operating Conditions (Notes 1, 2)
Supply Voltage (V
CC
) 4.5 VDCto 6.0 V
DC
Temperature Range T
MIN≤TA≤TMAX
ADC0844CCN, ADC0848BCN, 0˚C≤TA≤70˚C
ADC0848CCN
ADC0844BCJ, ADC0844CCJ, −40˚C≤T
A
≤85˚C
ADC0848BCV, ADC0848CCV
Electrical Characteristics
The following specifications apply for V
CC
=
5V
DC
unless otherwise specified.Boldface limits apply from T
MIN
to T
MAX
; all
other limits T
A
=
T
j
=
25˚C.
Parameter Conditions
ADC0844BCJ
ADC0844CCJ
ADC0844CCN
ADC0848BCN, ADC0848CCN
ADC0848BCV, ADC0848CCV
Limit
Units
Typ Tested Design Typ Tested Design
(Note 5) Limit Limit (Note 5) Limit Limit
(Note 6) (Note 7) (Note 6) (Note 7)
CONVERTER AND MULTIPLEXER CHARACTERISTICS
Maximum Total V
REF
=
5.00 V
DC
Unadjusted Error (Note 8)
ADC0844BCN, ADC0848BCN, BCV
±
1
⁄
2
±
1
⁄
2
LSB
ADC0844CCN, ADC0848CCN, CCV
±
1
±
1 LSB
ADC0844CCJ
±
1 LSB
Minimum Reference 2.4 1.1 2.4 1.2 1.1 kΩ
Input Resistance
Maximum Reference 2.4 5.9 2.4 5.4 5.9 kΩ
Input Resistance
Maximum Common-Mode (Note 9) V
CC
+0.05 VCC+0.05 VCC+0.05 V
Input Voltage
Minimum Common-Mode (Note 9) GND−0.05 GND−0.05 GND−0.05 V
Input Voltage
DC Common-Mode Error Differential Mode
±
1/16
±
1
⁄
4
±
1/16
±
1
⁄
4
±
1
⁄
4
LSB
Power Supply Sensitivity V
CC
=
5V
±
5
%
±
1/16
±
1
⁄
8
±
1/16
±
1
⁄
8
±
1
⁄
8
LSB
Off Channel Leakage (Note 10)
Current On Channel=5V, −1 −0.1 −1 µA
Off Channel=0V
On Channel=0V, 1 0.1 1 µA
Off Channel=5V
DIGITAL AND DC CHARACTERISTICS
V
IN(1)
, Logical “1” Input V
CC
=
5.25V 2.0 2.0 2.0 V
Voltage (Min)
V
IN(0)
, Logical “0” Input V
CC
=
4.75V 0.8 0.8 0.8 V
Voltage (Max)
I
IN(1)
, Logical “1” Input V
IN
=
5.0V 0.005 1 0.005 1 µA
Current (Max)
I
IN(0)
, Logical “0” Input
Current (Max)
V
IN
=
0V −0.005 −1 −0.005 −1 µA
V
OUT(1)
, Logical “1” V
CC
=
4.75V
Output Voltage (Min) I
OUT
=
−360 µA 2.4 2.8 2.4 V
I
OUT
=
−10 µA 4.5 4.6 4.5 V
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Page 4
Electrical Characteristics (Continued)
The following specifications apply for V
CC
=
5V
DC
unless otherwise specified.Boldface limits apply from T
MIN
to T
MAX
; all
other limits T
A
=
T
j
=
25˚C.
Parameter Conditions
ADC0844BCJ
ADC0844CCJ
ADC0844CCN
ADC0848BCN, ADC0848CCN
ADC0848BCV, ADC0848CCV
Limit
Units
Typ Tested Design Typ Tested Design
(Note 5) Limit Limit (Note 5) Limit Limit
(Note 6) (Note 7) (Note 6) (Note 7)
DIGITAL AND DC CHARACTERISTICS
V
OUT(0)
, Logical “0” V
CC
=
4.75V 0.4 0.34 0.4 V
Output Voltage (Max) I
OUT
=
1.6 mA
I
OUT
, TRI-STATE Output V
OUT
=
0V −0.01 −3 −0.01 −0.3 −3 µA
Current (Max) V
OUT
=
5V 0.01 3 0.01 0.3 3 µA
I
SOURCE
, Output Source V
OUT
=
0V −14 −6.5 −14 −7.5 −6.5 mA
Current (Min)
I
SINK
, Output Sink V
OUT
=
V
CC
16 8.0 16 9.0 8.0 mA
Current (Min)
I
CC
, Supply Current (Max) CS=1, V
REF
Open
1 2.5 1 2.3 2.5 mA
AC Electrical Characteristics
The following specifications apply for V
CC
=
5V
DC,tr
=
t
f
=
10 ns unless otherwise specified. Boldface limits apply from T
MIN
to T
MAX
; all other limits T
A
=
T
j
=
25˚C.
Tested Design
Parameter Conditions Typ Limit Limit Units
(Note 5) (Note 6) (Note 7)
t
C
, Maximum Conversion Time (See Graph) 30 40 60 µs
t
W(WR)
, Minimum WR Pulse Width (Note 11) 50 150 ns
t
ACC
, Maximum Access Time (Delay from Falling Edge of C
L
=
100 pF 145 225 ns
RD to Output Data Valid)
(Note 11)
t
1H,t0H
, TRI-STATE Control (Maximum Delay from Rising C
L
=
10 pF, R
L
=
10k 125 200 ns
Edge of RD to Hi-Z State)
(Note 11)
t
WI,tRI
, Maximum Delay from Falling Edge of WR or RD to (Note 11) 200 400 ns
Reset of INTR
tDS, Minimum Data Set-Up Time (Note 11) 50 100 ns
t
DH
, Minimum Data Hold Time (Note 11) 0 50 ns
C
IN
, Capacitance of Logic Inputs 5 pF
C
OUT
, Capacitance of Logic Outputs 5 pF
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. DC and AC electrical specifications do not apply when operating
the device beyond its specified operating conditions.
Note 2: All voltages are measured with respect to the ground pins.
Note 3: When the input voltage (V
IN
) at any pin exceeds the power supply rails (V
IN
<
V−or V
IN
>
V+) the absolute value of the current at that pin should be limited
to 5 mA or less. The 20 mA package input current limits the number of pins that can exceed the power supply boundaries witha5mAcurrent limit to four.
Note 4: Human body model, 100 pF discharged through a 1.5 kΩ resistor.
Note 5: Typicals are at 25˚C and represent most likely parametric norm.
Note 6: Tested limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).
Note 7: Design limits are guaranteed by not 100%tested. These limits are not used to calculate outgoing quality levels.
Note 8: Total unadjusted error includes offset, full-scale, linearity, and multiplexer error.
Note 9: For V
IN
(−) ≥ VIN(+) the digital output code will be 0000 0000. Two on-chip diodes are tied to each analog input, which will forward-conduct for analog input
voltages one diode drop below ground or one diode drop greater than V
CC
supply.Be careful during testing at low VCClevels (4.5V), as high level analog inputs (5V)
can cause this input diode to conduct, especially at elevated temperatures, and cause errors for analog inputs near full-scale. The spec allows 50 mV forward bias
of either diode. This means that as long as the analog V
IN
does not exceed the supply voltage by more than 50 mV, the output code will be correct. To achieve an
absolute 0 V
DC
to5VDCinput voltage range will therefore require a minimum supply voltage of 4.950 VDCover temperature variations, initial tolerance and loading.
Note 10: Off channel leakage current is measured after the channel selection.
Note 11: The temperature coefficient is 0.3%/˚C.
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Typical Performance Characteristics
Logic Input Threshold
Voltage vs Supply Voltage
DS005016-31
Output Current vs
Temperature
DS005016-32
Power Supply Current vs
Temperature
DS005016-33
Linearity Error vs V
REF
DS005016-34
Conversion Time vs V
SUPPLY
DS005016-35
Conversion Time vs
Temperature
DS005016-36
Unadjusted Offset Error vs
V
REF
Voltage
DS005016-37
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Page 6
TRI-STATE Test Circuits and Waveforms
Leakage Current Test Circuit
t
1H
DS005016-4
t1H,C
L
=
10 pF
DS005016-5
t
r
=
20 ns
t
0H
DS005016-6
t0H,C
L
=
10 pF
DS005016-7
t
r
=
20 ns
DS005016-8
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Timing Diagrams
Programming New Channel Configuration and Starting a Conversion
DS005016-9
Note 12: Read strobe must occur at least 600 ns after the assertion of interrupt to guarantee reset of INTR .
Note 13: MA stands for MUX address.
Using the Previously Selected Channel Configuration and Starting a Conversion
DS005016-10
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ADC0848 Functional Block Diagram
DS005016-11
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Page 9
Functional Description
The ADC0844 and ADC0848 contain a 4-channel and
8-channel analog input multiplexer (MUX) respectively. Each
MUX can be configured into one of three modes of operation
differential, pseudo-differential, and single ended. These
modes are discussed in the Applications Information Section. The specific mode is selected by loading the MUX address latch with the proper address (see
Table 1
and
Table
2
). Inputs to the MUX address latch (MA0-MA4) are common
with data bus lines (DB0-DB4) and are enabled when the RD
line is high.Aconversion is initiated via the CS and WR lines.
If the data from a previous conversion is not read, the INTR
line will be low. The falling edge of WR will reset the INTR
line high and ready the A/D for a conversion cycle. The rising
edge of WR, with RD high, strobes the data on the MA0/
DB0-MA4/DB4 inputs into the MUX address latch to select a
new input configuration and start a conversion. If the RD line
is held low during the entire low period of WR the previous
MUX configuration is retained, and the data of the previous
conversion is the output on lines DB0-DB7. After the conversion cycle (t
C
≤ 40 µs), which is set by the internal clock frequency, the digital data is transferred to the output latch and
the INTR is asserted low.Taking CS and RD low resets INTR
output high and outputs the conversion result on the data
lines (DB0-DB7).
Applications Information
1.0 MULTIPLEXER CONFIGURATION
The design of these converters utilizes a sampled-data comparator structure which allows a differential analog input to
be converted by a successive approximation routine.
The actual voltage converted is always the difference between an assigned “+” input terminal and a “−” input terminal.
The polarity of each input terminal of the pair being converted indicates which line the converter expects to be the
most positive. If the assigned “+” input is less than the “−” input the converter responds with an all zeros output code.
A unique input multiplexing scheme has been utilized to provide multiple analog channels. The input channels can be
software configured into three modes: differential, single
ended, or pseudo-differential.
Figure 1
shows the three
modes using the 4-channel MUX ADC0844. The eight inputs
of the ADC0848 can also be configured in any of the three
modes. In the differential mode, theADC0844 channel inputs
are grouped in pairs, CH1 with CH2 and CH3 with CH4. The
polarity assignment of each channel in the pair is interchangeable. The single-ended mode has CH1–CH4 assigned as the positive input with the negative input being the
analog ground (AGND) of the device. Finally, in the
pseudo-differential mode CH1–CH3 are positive inputs referenced to CH4 which is now a pseudo-ground. This
pseudo-ground input can be set to any potential within the input common-mode range of the converter.The analog signal
conditioning required in transducer-based data acquisition
systems is significantly simplified with this type of input flexibility. One converter package can now handle ground referenced inputs and true differential inputs as well as signals
with some arbitrary reference voltage.
The analog input voltages for each channel can range from
50 mV below ground to 50 mV above V
CC
(typically 5V) with-
out degrading conversion accuracy.
TABLE 1. ADC0844 MUX ADDRESSING
MUX Address CS WR RD Channel
#
MUX
MA3 MA2 MA1 MA0 CH1 CH2 CH3 CH4 AGND Mode
XLLLL H+−
XLLHL
L
H − + Differential
XLHLL H +−
XLHHL H −+
LHLLL H+ −
LHLHL
L
H + − Single-Ended
LHHLL H + −
LHHHL H + −
H H L L L H + − PseudoHHLHL
L
H + − Differential
HHHLL H +−
XXXXL
L
L Previous Channel Configuration
X=don’t care
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Applications Information (Continued)
2.0 REFERENCE CONSIDERATIONS
The voltage applied to the reference input of these converters defines the voltage span of the analog input (the difference between V
IN(MAX)
and V
IN(MIN)
) over which the 256
possible output codes apply. The devices can be used in either ratiometric applications or in systems requiring absolute
accuracy.The reference pin must be connected to a voltage
source capable of driving the minimum reference input resistance of 1.1 kΩ. This pin is the top of a resistor divider string
used for the successive approximation conversion.
In a ratiometric system (
Figure 2a
), the analog input voltage
is proportional to the voltage used for the A/D reference. This
voltage is typically the system power supply, so the V
REF
pin
can be tied to V
CC
. This technique relaxes the stability requirements of the system reference as the analog input and
A/D reference move together maintaining the same output
code for a given input condition.
For absolute accuracy (
Figure 2b
), where the analog input
varies between very specific voltage limits, the reference pin
can be biased with a time and temperature stable voltage
source. The LM385 and LM336 reference diodes are good
low current devices to use with these converters.
The maximum value of the reference is limited to the V
CC
supply voltage. The minimum value, however, can be quite
small (see Typical Performance Characteristics) to allow direct conversions of transducer outputs providing less than a
5V output span. Particular care must be taken with regard to
noise pickup, circuit layout and system error voltage sources
when operating with a reduced span due to the increased
sensitivity of the converter (1 LSB equals V
REF
/256).
3.0 THE ANALOG INPUTS
3.1 Analog Differential Voltage Inputs and
Common-Mode Rejection
The differential input of these converters actually reduces
the effects of common-mode input noise, a signal common
to both selected “+” and “−” inputs for a conversion (60 Hz is
most typical). The time interval between sampling the “+” input and then the “−” inputs is
1
⁄2of a clock period. The
change in the common-mode voltage during this short time
interval can cause conversion errors. For a sinusoidal
common-mode signal this error is:
where f
CM
is the frequency of the common-mode signal,
V
peak
is its peak voltage value and tCis the conversion time.
For a 60 Hz common-mode signal to generate a
1
⁄4LSB error
(≈5 mV) with the converter running at 40 µS, its peak value
would have to be 5.43V.Thislarge a common-mode signal is
much greater than that generally found in a well designed
data acquisition system.
4 Single-Ended
DS005016-12
2 Differential
DS005016-13
3 Pseudo-Differential
DS005016-14
Combined
DS005016-15
FIGURE 1. Analog Input Multiplexer Options
DS005016-38
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Applications Information (Continued)
TABLE 2. ADC0848 MUX Addressing
MUX Address CS WR RD Channel MUX
MA4 MA3 MA2 MA1 MA0 CH1 CH2 CH3 CH4 CH5 CH6 CH7 CH8 AGND Mode
XLLLLL H+−
XLLLHL H−+
XLLHLL H +−
XLLHHL
L
H − + Differential
XLHLLL H +−
XLHLHL H −+
XLHHLL H +−
XLHHHL H −+
LHLLLL H+ −
LHLLHL H + −
LHLHLL H + −
LHLHHL
L
H + − Single-Ended
LHHLLL H + −
LHHLHL H + −
LHHHLL H + −
LHHHHL H + −
HHLLLL H+ −
HHL LHL H + −
HHLHLL H + − PseudoHHLHHL
L
H + − Differential
HHHL LL H + −
HHHLHL H + −
HHHHLL H +−
XXXXXL
L
L Previous Channel Configuration
3.2 Input Current
Due to the sampling nature of the analog inputs, short duration spikes of current enter the “+” input and exit the “−” input
at the clock edges during the actual conversion. These currents decay rapidly and do not cause errors as the internal
comparator is strobed at the end of a clock period. Bypass
capacitors at the inputs will average these currents and
cause an effective DC current to flow through the output resistance of the analog signal source. Bypass capacitors
should not be used if the source resistance is greater than
1kΩ.
3.3 Input Source Resistance
The limitation of the input source resistance due to the DC
leakage currents of the input multiplexer is important. A
worst-case leakage current of
±
1 µA over temperature will
createa1mVinput error witha1kΩsource resistance. An
op amp RC active low pass filter can provide both impedance buffering and noise filtering should a high impedance
signal source be required.
4.0 OPTIONAL ADJUSTMENTS
4.1 Zero Error
The zero of the A/D does not require adjustment. If the minimum analog input voltage value, V
IN(MIN)
, is not ground, a
zero offset can be done. The converter can be made to out-
put 0000 0000 digital code for this minimum input voltage by
biasing any V
IN
(−) input at this V
IN(MIN)
value. This is useful
for either differential or pseudo-differential modes of input
channel configuration.
The zero error of the A/D converter relates to the location of
the first riser of the transfer function and can be measured by
grounding the V
−
input and applying a small magnitude posi-
tive voltage to the V
+
input. Zero error is the difference between actual DC input voltage which is necessary to just
cause an output digital code transition from 0000 0000 to
0000 0001 and the ideal
1
⁄2LSB value (1⁄2LSB=9.8 mV for
V
REF
=
5.000 V
DC
).
4.2 Full-Scale
The full-scale adjustment can be made by applying a differential input voltage which is 1
1
⁄2LSB down from the desired
analog full-scale voltage range and then adjusting the magnitude of the V
REF
input for a digital output code changing
from 1111 1110 to 1111 1111.
4.3 Adjusting for an Arbitrary Analog Input Voltage
Range
If the analog zero voltage of the A/D is shifted away from
ground (for example, to accommodate an analog input signal
which does not go to ground), this new zero reference
should be properly adjusted first. A V
IN
(+) voltage which
equals this desired zero reference plus
1
⁄2LSB (where the
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Page 12
Applications Information (Continued)
LSB is calculated for the desired analog span, 1 LSB=analog span/256) is applied to selected “+” input and the zero
reference voltage at the corresponding “−” input should then
be adjusted to just obtain the 00
HEX
to 01
HEX
code transition.
The full-scale adjustment should be made [with the proper
V
IN
(−) voltage applied] by forcing a voltage to the VIN(+) in-
put which is given by:
where V
MAX
=
the high end of the analog input range and
V
MIN
=
the low end (the offset zero) of the analog range. (Both
are ground referenced.)
The V
REF
(or VCC) voltage is then adjusted to provide a code
change from FE
HEX
to FF
HEX
. This completes the adjust-
ment procedure.
For an example see the Zero-Shift and Span Adjust circuit
below.
DS005016-16
a) Ratiometric
DS005016-17
b) Absolute with a Reduced Span
FIGURE 2. Referencing Examples
Zero-Shift and Span Adjust (2V≤V
IN
≤5V)
DS005016-18
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Applications Information (Continued)
Differential Voltage Input 9-Bit A/D
DS005016-19
Span Adjust (0V≤VIN≤3V)
DS005016-20
Protecting the Input
DS005016-21
Diodes are 1N914
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Applications Information (Continued)
High Accuracy Comparators
DS005016-22
DO=all 1s if VIN(+)>VIN(−)
DO=all 0s if V
IN
(+)<VIN(−)
Operating with Automotive Ratiometric Transducers
DS005016-23
*VIN(−)=0.15 V
CC
15%of VCC≤V
XDR
≤85%of V
CC
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Applications Information (Continued)
A Stand Alone Circuit
DS005016-25
Note: DUT pin numbers in parentheses are for ADC0844, others are for ADC0848.
Start a Conversion without Updating the Channel Configuration
DS005016-26
CS•WR will update the channel configuration and start a conversion.
CS•RD will read the conversion data and start a new conversion without updating the channel configuration.
Waiting for the end of this conversion is not necessary. A CS•WR can immediately follow the CS•RD .
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Applications Information (Continued)
SAMPLE PROGRAM FOR ADC0844 — INS8039 INTERFACE
CONVERTING TWO RATIOMETRIC, DIFFERENTIAL SIGNALS
ORG 0H
0000 04 10 JMP BEGIN ;START PROGRAM AT ADDR 10
ORG 10H ;MAIN PROGRAM
0010 B9 FF BEGIN: MOV R1,
#
0FFH ;LOAD R1 WITH A UNUSED ADDR
;LOCATION
0012 B8 20 MOV R0,
#
20H ;A/D DATA ADDRESS
0014 89 FF ORL P1,
#
0FFH ;SET PORT 1 OUTPUTS HIGH
0016 23 00 MOV A,00H ;LOAD THE ACC WITH A/D MUX DATA
;CH1 AND CH2 DIFFERENTIAL
0018 14 50 CALL CONV ;CALL THE CONVERSION SUBROUTINE
001A 23 02 MOV A,
#
02H ;LOAD THE ACC WITH A/D MUX DATA
;CH3 AND CH4 DIFFERENTIAL
001C 18 INC R0 ;INCREMENT THE A/D DATA ADDRESS
001D 14 50 CALL CONV ;CALL THE CONVERSION SUBROUTINE
;CONTINUE MAIN PROGRAM
;CONVERSION SUBROUTINE
;ENTRY:ACC—A/D MUX DATA
;EXIT: ACC— CONVERTED DATA
ORG 50H
0050 99 FE CONV: ANL P1,
#
0FEH ;CHIP SELECT THE A/D
0052 91 MOVX
@
R1,A ;LOAD A/D MUX & START CONVERSION
0053 09 LOOP: IN A,P1 ;INPUT INTR STATE
ADC0844—INS8039 Interface
DS005016-27
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Applications Information (Continued)
SAMPLE PROGRAM FOR ADC0844—INS8039 INTERFACE
CONVERTING TWO RATIOMETRIC, DIFFERENTIAL SIGNALS (Continued)
0054 32 53 JB1 LOOP ;IF INTR=1 GOTO LOOP
0056 81 MOVX A,@R1 ;IF INTR=0 INPUT A/D DATA
0057 89 01 ORL P1,&01H ;CLEAR THE A/D CHIP SELECT
0059 A0 MOV
@
R0,A ;STORE THE A/D DATA
005A 83 RET ;RETURN TO MAIN PROGRAM
SAMPLE PROGRAM FOR ADC0848 — NSC800 INTERFACE
0008 NCONV EQU 16
000F DEL EQU 15 ;DELAY 50 µsec CONVERSION
001F CS EQU 1FH ;THE BOARD ADDRESS
3C00 ADDTA EQU 003CH ;START OF RAM FOR A/D
;DATA
0000' 08 09 0A 0B MUXDTA: DB 08H,09H,0AH,0BH ;MUX DATA
0004' 0C 0D 0E 0F DB 0CH,0DH,0EH,0FH
0008' 0E 1F START: LD C,CS
000A' 06 16 LD B,NCONV
000C' 21 0000' LD HL,MUXDTA
000F' 11 003C LD DE,ADDTA
0012' ED A3 STCONV: OUTI ;LOAD A/D’S MUX DATA
;AND START A CONVERSION
0014' EB EX DE,HL ;HL=RAM ADDRESS FOR THE
;A/D DATA
0015' 3E 0F LD A,DEL
0017' 3D WAIT: DEC A ;WAIT 50 µsec FOR THE
0018' C2 0013' JP NZ,WAIT ;CONVERSION TO FINISH
001B' ED A2 INI ;STORE THE A/D’S DATA
;CONVERTED ALL INPUTS?
001D' EB EX DE,HL
001E' C2 000E' JP NZ,STCONV ;IF NOT GOTO STCONV
END
Note 14: This routine sequentially programs the MUX data latch in the signal-ended mode. For CH1-CH8 a conversion is started, then a 50 µs wait for the A/D to
complete a conversion and the data is stored at address ADDTA for CH1, ADDTA + 1 for CH2, etc.
I/O Interface to NSC800
DS005016-28
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ADC0844/ADC0848 8-Bit µP Compatible A/D Converters with Multiplexer Options
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